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24 April 2024 |
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Investigating The Possible Anomaly Between Nebular and Stellar Oxygen Abundances in the Dwarf Irregular Galaxy WLM | | Henry Lee
; Evan D. Skillman
; Kim A. Venn
; | | Date: |
26 Oct 2004 | | Journal: | Astrophys.J. 620 (2005) 223-237 | | Subject: | astro-ph | | Affiliation: | 2,1) ( University of Minnesota, Macalester College | | Abstract: | We obtained new optical spectra of 13 H II regions in WLM with EFOSC2; oxygen abundances are derived for nine H II regions. The temperature-sensitive [O III] 4363 emission line was measured in two bright H II regions HM7 and HM9. The direct oxygen abundances for HM7 and HM9 are 12+log(O/H) = 7.72 +/- 0.04 and 7.91 +/- 0.04, respectively. We adopt a mean oxygen abundance of 12+log(O/H) = 7.83 +/- 0.06. This corresponds to [O/H] = -0.83 dex, or 15% of the solar value. In H II regions where [O III] 4363 was not measured, oxygen abundances derived with bright-line methods are in general agreement with direct values of the oxygen abundance to an accuracy of about 0.2 dex. In general, the present measurements show that the H II region oxygen abundances agree with previous values in the literature. The nebular oxygen abundances are marginally consistent with the mean stellar magnesium abundance ([Mg/H] = -0.62). However, there is still a 0.62 dex discrepancy in oxygen abundance between the nebular result and the A-type supergiant star WLM15 ([O/H] = -0.21). Non-zero reddening values derived from Balmer line ratios were found in H II regions near a second H I peak. There may be a connection between the location of the second H I peak, regions of higher extinction, and the position of WLM15 on the eastern side of the galaxy. | | Source: | arXiv, astro-ph/0410640 | | Services: | Forum | Review | PDF | Favorites | |
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